An in-band full-duplex radio receiver with a passive vector modulator downmixer for self-interference cancellation

In-band full-duplex (FD) wireless, i.e., simultaneous transmission and reception at the same frequency, introduces strong self-interference (SI) that masks the signal to be received. This paper proposes a receiver in which a copy of the transmit signal is fed through a switched-resistor vector modulator (VM)that provides simultaneous downmixing, phase shift, and amplitude scaling and subtracts it in the analog baseband for up to 27 dB SI-cancellation. Cancelling before active baseband amplification avoids self-blocking, and highly linear mixers keep SIinduced distortion low, for a receiver SI-to-noise-and-distortionratio (SINDR) of up to 71.5 dB in 16.25 MHz BW. When combined with a two-port antenna with only 20 dB isolation, the low RX distortion theoretically allows sufficient digital cancellation for over 90 dB link budget, sufficient for short-range, low-power FD links.